In a conventional backlight of a large-sized liquid crystal display apparatus, a number of cold cathode tubes are disposed immediately below a liquid crystal panel, and these cold cathode tubes are used with other members such as a diffusing plate and a reflecting plate. In recent years, light emitting diodes (hereinafter referred to as “LEDs”) have been used as light sources for backlights. LEDs have increased their efficiency recently, and are expected to serve as low-power light sources to replace fluorescent lamps. In the case where LEDs are used as a light source in a liquid crystal display apparatus, the power consumption of the apparatus can be reduced by controlling the brightness of the LEDs according to an image to be displayed.
In a backlight of a liquid crystal display apparatus using LEDs as a light source, a large number of LEDs are disposed therein instead of cold cathode tubes. The use of a large number of LEDs allows the entire surface of the backlight to have uniform brightness, but the need for such a large number of LEDs is an obstacle to cost reduction. Attempts have been made to increase the output power of each LED to reduce the required number of LEDs. For example, Patent Literature 1 has proposed a lens that is designed to provide a uniform surface light source with a reduced number of LEDs.
In order to obtain a uniform surface light source with a reduced number of LEDs, the area to be illuminated by light emitted from each LED needs to be increased. That is, light emitted from each LED needs to be spread to obtain a wider range of light transmission directions of the LED. For this purpose, in Patent Literature 1, a lens having a circular shape in plan view is disposed on an LED as a chip to control the light transmission directions of the LED chip. The light exit surface of this lens, through which light exits the lens, has a shape such that a portion in the vicinity of the optical axis is a concave surface and a portion outside the concave surface is a convex surface extending continuously from the concave surface.